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At least 217 records · Page 12Linked to original sources
PubMed1996

Effects of accelerated eruption on the enamel of the rat lower incisor.

The effect of accelerated eruption of the rat lower incisor on enamel was studied in a series of segments obtained when the incisor was cut repeatedly out of occlusion over a five-week period. The segments were ground, cleaned, acid-etched, observed with SEM, and analyzed with EDX. Pigmentation was lost within 11 days. Pigmented superficial enamel was more acid-resistant than the rest of the enamel, but this quality decreased with decreasing iron content. Hypomineralized enamel first appeared in a restricted area at the mesio-labial angle of the tooth in the 6th-7th segment obtained after 11-14 days. Later, hypomineralization became more generalized. All enamel zones were retained throughout the experiment. The geometry of the prism pattern was affected. The angle between prism rows and the enamel-dentin junction increased from 44 degrees to 48 degrees, while the angle of decussation increased from 60 degrees to 70 degrees. The angle between the enamel surface and prisms in the outer enamel was more difficult to assess, but tended to increase from about 25 degrees to 29 degrees. However, the prisms retained their incisal direction. The connection between enamel and dentin was partly disrupted from about the 9th segment onward. The depth of the mesial concavity of the enamel-dentin junction decreased from about the 10th segment onward. Accelerated eruption affects all stages of enamel formation and is a suitable and predictable model for studying regulatory mechanisms in amelogenesis.

Ameloblasts↗
PubMed1997

Major topics in quantitative microradiography of enamel and dentin: R parameter, mineral distribution visualization, and hyper-remineralization.

Three aspects of quantitative transverse microradiography are described and discussed: (1) the average mineral loss parameter of enamel or dentin lesions (R) in vol%; (2) mineral distribution visualization of lesions by means of a computer-assisted videodensitometric (CAV) method; and (3) the microradiography of hyper-remineralized lesions. "R", defined as the average amount of mineral lost (or gained) in a lesion per unit lesion length, is a useful parameter in dental caries. The results show that, in vitro, R is about constant over the demineralization period for enamel and dentin. This was found even for quite different dissolution kinetics. R is strongly reduced by the presence of small amounts of fluoride in the demineralizing system. R of dentin lesions is smaller than for enamel lesions. We conclude that the mineral loss value (delta Z) and the lesion depth (ld) are in general dependent parameters during in vitro or in situ studies on enamel or dentin. During lesion formation, mineral loss from the lesion and acid penetration in the tissue are obviously linked. This is possible only if the mineral content in the lesion does not change very much after passage of the lesion front. The CAV method presented is illustrated for enamel lesions formed in vitro and in situ.

Absorptiometry, Photon↗
PubMed1997

The relationship between surface free-energy and kinetics in the mineralization and demineralization of dental hard tissue.

The interfacial free-energy is an important factor in the regulation of mineralization and dissolution at the surfaces of dental hard tissues. However, few thermodynamic studies have been aimed at the elucidation of the interfacial terms. Contact angle measurements (sessile drop and thin layer wicking) and kinetic dissolution and growth techniques have been used to study the interfacial properties of root dentin (D), human enamel (E), and hydroxyapatite (HAP). The interfacial tensions between water (w) and each of these phases were calculated from contact angle data according to surface tension components theory. The values gamma wD = 4.5 x 10(-3) J m-2, gamma wE = 8.8 x 10(-3) J m-2, and gamma w,HAP = 10.4 x 10(-3) J m-2 were of the same order of magnitude as those obtained from dissolution kinetic data (pH = 4.5): gamma wD = 1.4 x 10(-3) J m-2, gamma wE = 3.2 x 10(-3) J m-2, and gamma wHAP = 9.3 x 10(-3) J m-2. Kinetics studies of the crystallization of HAP on HAP, dentin, and enamel yielded the interfacial free-energy values, gamma wHAP = 17.1 x 10(-3) J m-2, 17.7 x 10(-3) J m-2, and 9.4 x 10(-3) J m-2, respectively, probably reflecting the interfacial energies of the deposited phases rather than those of the dental hard-tissue substrata. The lower interfacial tension values are consistent with the higher solubilities of these solid phases: logKSO = -52.0, -55 approximately 57, and -58 approximately 59, for root dentin, enamel, and HAP, respectively, expressed as an equivalent HAP ionic product. The higher interfacial free-energy is also consistent with the slower mineralization of HAP on dentin and enamel surfaces.

Crystallization↗
PubMed1997

The effect of fluoride on apatite structure and growth.

Fluoride participates in many aspects of calcium phosphate formation in vivo and has enormous effects on the process and on the nature and properties of formed mineral. The most well-documented effect of fluoride is that this ion substitutes for a column hydroxyl in the apatite structure, giving rise to a reduction of crystal volume and a concomitant increase in structural stability. In the process of enamel mineralization during amelogenesis (a unique model for the cell-mediated formation of well-crystallized carbonatoapatite), free fluoride ions in the fluid phase are supposed to accelerate the hydrolysis of acidic precursor(s) and increase the driving force for the growth of apatitic mineral. Once fluoride is incorporated into the enamel mineral, the ion likely affects the subsequent mineralization process by reducing the solubility of the mineral and thereby modulating the ionic composition in the fluid surrounding the mineral, and enhancing the matrix protein-mineral interaction. But excess fluoride leads to anomalous enamel formation by retarding tissue maturation. It is worth noting that enameloid/enamel minerals found in vertebrate teeth have a wide range of CO3 and fluoride substitutions. In the evolutionary process from elasmobranch through enameloid to mammalian enamel, the biosystems appear to develop regulatory functions for limiting the fluoridation of the formed mineral, but this development is accompanied by an increase of carbonate substitution or defects in the mineral. In research on the cariostatic effect of fluoride, considerable emphasis is placed on the roles of free fluoride ions (i.e., preventing the dissolution and accelerating the kinetics of remineralization) in the oral fluid bathing tooth mineral. Fluoride also has been used for the treatment of osteoporosis, but much still remains to be learned about maximizing the benefit and minimizing the risk of fluoride when used as a public health measure.

Amelogenesis↗
PubMed1998

Cellular and chemical events during enamel maturation.

This review focuses on the process of enamel maturation, a series of events associated with slow, progressive growth in the width and thickness of apatitic crystals. This developmental step causes gradual physical hardening and transformation of soft, newly formed enamel into one of the most durable mineralized tissues produced biologically. Enamel is the secretory product of specialized epithelial cells, the ameloblasts, which make this covering on the crowns of teeth in two steps. First, they roughly "map out" the location and limits (overall thickness) of the entire extracellular layer as a protein-rich, acellular, and avascular matrix filled with thin, ribbon-like crystals of carbonated hydroxyapatite. These initial crystals are organized spatially into rod and interrod territories as they form, and rod crystals are lengthened by Tomes' processes in tandem with appositional movement of ameloblasts away from the dentin surface. Once the full thickness of enamel has been formed, ameloblasts initiate a series of repetitive morphological changes at the enamel surface in which tight junctions and deep membrane infoldings periodically appear (ruffle-ended), then disappear for short intervals (smooth-ended), from the apical ends of the cells. As this happens, the enamel covered by these cells changes rhythmically in net pH from mildly acidic (ruffle-ended) to near-physiologic (smooth-ended) as mineral crystals slowly expand into the "spaces" (volume) formerly occupied by matrix proteins and water. Matrix proteins are processed and degraded by proteinases throughout amelogenesis, but they undergo more rapid destruction once ameloblast modulation begins. Ruffle-ended ameloblasts appear to function primarily as a regulatory and transport epithelium for controlling the movement of calcium and other ions such as bicarbonate into enamel to maintain buffering capacity and driving forces optimized for surface crystal growth. The reason ruffle-ended ameloblasts become smooth-ended periodically is unknown, although this event seems to be crucial for sustaining long-term crystal growth.

Ameloblasts↗
PubMed2004

Opg, Rank, and Rankl in tooth development: co-ordination of odontogenesis and osteogenesis.

Osteoprotegerin (OPG), receptor activator of nuclear factor-kappaB (RANK), and RANK ligand (RANKL) are mediators of various cellular interactions, including bone metabolism. We analyzed expression of these three genes during murine odontogenesis from epithelial thickening to cytodifferentiation stages. Opg showed expression in the thickening and bud epithelium. Expression of Opg and Rank was observed in both the internal and the external enamel epithelium as well as in the dental papilla mesenchyme. Although Rankl expression was not detected in tooth epithelium or mesenchyme, it was expressed in pre-osteogenic mesenchymal cells close to developing tooth germs. All three genes were detected in developing dentary bone at P0. The addition of exogenous OPG to explant cultures of tooth primordia produced a delay in tooth development that resulted in reduced mineralization. We propose that the spatiotemporal expression of these molecules in early tooth and bone primordia cells has a role in co-ordinating bone and tooth development.

Alveolar Process↗
PubMed2005

Hyper-expression of osteocalcin mRNA in odontoblasts of Hyp mice.

The Hyp mouse is a murine homologue of human X-linked hypophosphatemia that displays hypo-mineralization in bone and dentin. In this study, we tested the hypothesis that the defect in Hyp mice leads to alterations in the expression of dentin matrix proteins that may be associated with the hypo-mineralization changes in the tissues. Quantitative RT-PCR analyses showed that expression of the osteocalcin gene in Hyp mice tooth germ samples was significantly higher than in wild-type mice, whereas the gene expressions of osteonectin, osteopontin, dentin matrix protein 1, and type I collagen in both types of mice were similar. Further, cultured Hyp mice tooth germ samples exhibited a higher expression of the osteocalcin gene than did those from wild-type mice, which was in accord with the results of our in vivo analysis. These findings suggest that osteocalcin mRNA is highly expressed in Hyp mice odontoblasts and may be associated with dentin hypo-mineralization.

Animals↗
PubMed1995

[Pharmacological study of tooth formation and mineralization using a tooth germ cultivation system].

In this study, we introduce a cultivation method for mandibular first molars from mouse embryos. We also investigate the in vitro effects of several drugs on tooth formation. Histological observations demonstrated that the tooth germ dissected from 17-day-old embryonic mice and cultivated for 7 days under the conditions described here showed clear mineralization in the dentin and enamel. Alkaline phosphatase (ALP) activity and calcium content in the tooth germ increased developmentally during 7-day cultivation. The increase of calcium was preceded by that of ALP in the germ. The removal of ALP attached covalently to the external surface of plasma membranes by phosphatidylinositol specific phospholipase C disturbed in vitro mineralization in the tooth germ, suggesting that ALP functioning as an ectoenzyme is involved in the physiological process of tooth formation. To elucidate the effects of calcium regulating hormones and several drugs on tooth mineralization, ALP and calcium content were measured and also the tooth germ was observed histologically. The results obtained from the present study suggest that this in vitro system provides a useful tool for investigating both the direct action of drugs on tooth formation and the mechanisms of drug action.

Alkaline Phosphatase↗
PubMed1991

[In vitro effect of chlorpromazine on the mineralization of tooth germ in mice--comparison with that of retinoic acid and HEBP].

Effects of chlorpromazine on the mineralization and alkaline phosphatase activity (ALP) in the tooth germ were examined and compared with those of retinoic acid and HEBP (1-hydroxyethylidene-1, 1-bisphosphonate). Mandibular first molars from 17-day-old mouse embryos were cultured with or without drugs. Calcium content and ALP in the tooth germ increased gradually from 0 to 7 days in culture, the increase of calcium being preceded by that of ALP. Retinoic acid suppressed increases of calcium and ALP in the tooth germ but not in the specimens precultured for 2 days, suggesting that retinoic acid inhibits the mineralization at an early developmental stage of the tooth. HEBP, a physiochemical inhibitor of mineralization, suppressed the increase of calcium, but significantly enhanced the increased of ALP in the tooth germ. Chlorpromazine, which has an antagonistic action towards calmodulin, also suppressed the increases of calcium and ALP in the tooth germ. Calmodulin antagonists W-7 and W-5 similarly suppressed the increases of calcium and ALP; W-5 had less effects on both calcium and ALP. These results indicate that calmodulin may be involved in the regulation of the mineralization in the tooth germ. These drugs are shown to possess different modes of inhibitory action on the mineralization.

Alkaline Phosphatase↗
PubMed2001

Study of the maturation of the organic (type I collagen) and mineral (nonstoichiometric apatite) constituents of a calcified tissue (dentin) as a function of location: a Fourier transform infrared microspectroscopic investigation.

Fourier transform infrared microspectroscopy (FTIRM) was used to investigate the organic and mineral phases of a calcified tissue (dentin) as a function of its location from predentin toward enamel. Thin dentin slices (decalcified or not) were fixed in formaldehyde and embedded in glycolmethylmethacrylate (GMA). Fixation did not denature collagen, and GMA did not interact with organic or mineral constituents of dentin. The v1v3 PO4 domain was studied in particular in order to estimate mineral maturity and amide I, II, A, and B to obtain data on protein conformation. The results showed that dentin apatite became increasingly mature (stoichiometric) from the mineralization front toward the enamel, especially through loss of HPO4(2-) groups and vacancies. Moreover, collagen fibrils became less and less hydrated, suggesting that intrafibrillar mineralization partially dehydrated the collagen. Combined study of the organic and mineral fractions of calcified tissues may help clarify their relationships in physiological and pathological tissues.

Adolescent↗
PubMedDate not supplied

[Effect of sucrose-containing gum and fluoridated dentifrice on in situ remineralization of artificial caries].

The aim of this study was to evaluate the remineralization of incipient carious lesions in bovine enamel in situ. Artificial carious lesions were produced and fixed in removable lower appliances in the region of the lingual surfaces of first molars, in six volunteers with ages between 18 and 22 years, who were subjected to 3 distinct experimental periods of 1 week each. In the first period (control group), patients brushed their teeth with a non-fluoridated dentifrice 4 times a day (after meals), and, in the second period (group I), patients used a dentifrice containing 1,500 ppm of fluorine (in the form of MFP). In the third period (group II) volunteers brushed their teeth with non-fluoridated dentifrice and used chewing gum containing 60% of sucrose during 20 minutes, 4 times a day (after meals). Before and after each treatment, the specimens underwent Vicker's hardness test (200 g of load), and the remineralization percentage (alpha) was calculated. The control group showed 2.78% of demineralization, and groups I and II showed 3.36 and 5.21% of remineralization, respectively. Statistical analysis (with Kruskal-Wallis and Miller's tests) showed significant difference (p < 0.05) between the control and experimental groups (I and II). Group II showed greater alpha than group I, but this difference was not significant. These results suggest that the use of sucrose-containing chewing gum and fluoridated dentifrice has a considerable effect on the remineralization of incipient carious lesions and may be a valuable alternative for their prevention.

Adolescent↗
PubMed2003

Retarded eruption of maxillary second premolars associated with late development of the germs.

This study focused on five unusual cases with anomalous eruptions of the maxillary second premolars that related to late development of the germs. In four cases, the affected premolars erupted between the ages of 12y3m and 14y6m. In one case, which was suspected to include bilateral anomalies, the eruption of the premolar was excessively late, continuing up to 17y8m old. It was surmised that the degree of tooth formation in the contralateral side might help to predict approximately at what age the late premolars will erupt.

Adolescent↗
PubMed1979

The hypermineralization of diseased root surfaces.

Root surfaces which have lost their attachment due to chronic inflammatory periodontal disease present significant increases in calcium, magnesium, phosphorus, and fluoride. The clinical significance of this effect is not known in regards to wound healing, but it may be helpful in control of cervical sensitivity.

Adolescent↗